As more and more electronic devices are made with digital controls; and as the devices become smaller and smaller, the need for impulse actuators that can operate on low average power has steadily increased. There are very few basic mechanisms that can efficiently translate an electrical impulse into linear mechanical motion. A requirement that the motion be silent, makes the design even more difficult; and eliminates most of the electromechanical devices now being used.
The most common electrical device for deriving linear motion is the solenoid coil, with a moving core plug. It is, however, very inefficient because of the large starting air gap involved; and the core of the solenoid makes a great deal of noise when it reaches the end of travel. The movement of the core is very quick but with very little starting force; consiquently, it cannot store its force over a period of time, and transfer the energy slowly into a high inertia load.
There are rotary solenoids which translate a lateral core motion, through balls in a sloped race, into a rotational motion, of the order of 20 to 30 degrees. This type does have the ability to store energy during the rotation; however, it must return to the starting position by spring loading, which robs it of useable power during the power stroke; and this type of rotary solenoid is also very noisy.
It is, therefore, one object of this invention to provide an efficient D.C.Impulse Actuator System which, with an added brush contact to the armature of a small D.C. motor and suitable drive circuitry, can be used as a relatively silent single turn rotary actuator; which, with the use of a suitable 360 degree rotating cam, can produce a single in line drive motion from each electrical start pulse.
Most magnetically actuated devices at present , such as the solenoid and relay type mechanisms, have power curves that are inversely proportional (by square law) to the size of the magnetic air gap. Consequently, the start-up or stall power drops off quickly as the required distance of movement is increased.
It is, therefore, another object of the invention to utilize the efficient design of a conventional D.C. motor, which has the advantage (1) a very small air gap between the armature poles and the field magnets; and (2) an efficient build up of inertia as the armature speed builds up; with a round cam which delivers maximum output at 180 degrees rotation; and utilizes the energy that is stored in the armature to drive a load over a relatively long portion of the cycle.
In many cases, such as in miniature pumps, the required power to the pump builds up as the actuating stroke nears its end of travel--much as with the piston of a car motor as it approaches top dead center.
It is yet another object of this invention to provide an integrated Impulse Drive System that is easily adaptable to miniature devices, and that combines the characteristics of the single turn D.C. Motor Actuator, and the cosine characteristic of a round rotating cam, as the matched elements of a silent, single stroke, in-line actuator.
One of the primary advantages of impulse actuated mechanisms, and particularly when the impulses are needed at relatively slow rates, is the low average power requirement; because the power can be completely off between impulses. This requirement is especially acute when the equipment incorporating the drive element is to be portable and battery operated. When using battery operated equipment it is also desirable to have the mechanical element self regulating, so that it will not be necessary to use power wasting series regulation to overcome the natural decay of voltage as the batteries are being used.
It is, therefore, an important object of this system invention to have integrated control circuitry that is normally off between impulses, and which has the means to detect the position of the single turn motor and its associated rotating cam at the end-of-drive point, to signal the beginning of the braking cycle; this type of feedback permitting a decay in battery voltage, as well as normal variations in the load conditions.
The combined features of the Impulse Actuator System, based on the Motor Actuator in copending application Ser. No. 917,005, will be more completely outlined in the following drawings, and operational description: